How the Sun Works. Presented by the

Transcription

1 How the Sun Works Presented by the

2 The Sun warms our planet every day, provides the light by which we see and is absolutely necessary for life on Earth. In this presentation, we will examine the fascinating world of our nearest star. We will look at the parts of the sun, the amazing way it makes light and heat, and its major features.

3 Because we see the sun everyday, we tend to take it for granted. But if you think about it, you may have some questions such as: If the sun is in the vacuum of space, how does it burn? What keeps all that gas from leaking into space? How big is the sun? Why does it send out solar flares? When will it stop burning? Is the sun like other stars?

4 The sun is a star, just like the other stars we see at night. The difference is distance the other stars are light years away, while our sun is only about 8 light minutes away. (93 Million Miles or 1 AU)

5 Light Year A light year is a way of measuring distance. A light year is the distance that light travels in 1 year. Light travels at 186,000 miles per second. 186,000 miles/second*60 seconds/minute*60 minutes/hour*24 hours/day*365 days/year = 5,865,696,000,000 miles/year. ( 6 Trillion Miles )

6 Spectrum Officially, the sun is classified as a G2 Main Sequence type star based on its temperature and the spectrum of light it emits. The sun is an average star, merely one of billions of stars that orbit the center of our galaxy.

7 The sun has burned for more than 4.5 billion years and will continue to do so for another 4 or 5 billion years. It is a massive collection of gas, mostly hydrogen and helium. Because it is so massive, it has immense gravity, enough gravitational force to hold all of the hydrogen and helium together (and to hold all of the planets in their orbits around the sun.

8 Parts of the Sun The sun is made of gas and has no solid surface as Earth does. However, it still has a defined structure. The 3 major surface areas: Core Radiative Zone Convective Zone

9 Above the surface of the sun is its atmosphere, which consists of three parts. Photosphere Chromosphere Corona

10 The sun does not burn like wood burns. Instead the sun is a gigantic nuclear reactor. We will see that all of the major features of the sun can be explained by the nuclear reactions that make its energy, the magnetic fields that are caused by the movements of the gas, and the immense gravity.

11 The Core The core starts from the center and extends to 25 percent of the sun s radius. Here gravity pulls all of the mass inward and creates intense pressure. The pressure is high enough to force atoms of hydrogen to come together in nuclear fusion reactions. Two atoms of hydrogen are combined to create helium-4 and energy in several steps:

12 1. Two protons combine to form a deuterium atom. 2. A proton and a deuterium atom combine to form a helium-3 atom and a gamma ray. 3. Two helium-3 atoms combine to form a helium-4 atom

13 These reactions account for 85 percent of the sun s energy. The remaining 15 percent comes from the following reactions. A helium-3 atom and a helium-4 atom combine to form a beryllium-7 atom and a gamma ray. A beryllium-7 atom captures an electron to become lithium-7 and a neutrino. The lithium-7 combines with a proton to form two helium-4 atoms.

14 E=mc 2 The helium-4 atoms are less massive than the two hydrogen atoms that started the process, so the difference in mass was converted to energy as described by Einstein s theory of relativity. Energy = mass X 186,000^2 The sun s energy output is (3.86e33 ergs/second) or 386 billion billion megawatts. 1 erg is the amount of energy to move 1 gram 1 centimeter. 600 million tons of Hydrogen are converted to helium every second.

15 Radiative Zone The radiative zone extends 55 percent of the sun s radius from the core. In this zone, the energy from the core is carried outward by photons. The photons are absorbed and re-emitted many times by gas molecules before a photon made in the core reaches the surface.

16 These convection currents are rising movements of hot gas next to falling movements of cool gas, much like what you see if you placed glitter in a simmering pot of water. Convective Zone The convective zone, which is the final 20 percent of the sun s radius, is dominated by convection currents that carry the energy outward to the surface.

17 Sun s Atmosphere The photosphere is the lowest region of the sun s atmosphere and is the region that can be seen from Earth. It is miles wide and has an average temperature of 5,800 degrees Kelvin. ( degrees Fahrenheit) It appears bubbly or granulated. The bumps are the upper surfaces of the convection current cells beneath and each granulation can be 600 miles wide.

18 Chromosphere The chromosphere lies above the photosphere to about 1,200 miles. The temperature rises across the chromosphere from 4,500 degrees Kelvin to about 10,000 degrees Kelvin. As gases churn in the photosphere, they produce shock waves that heat the surrounding gas and send it piercing through the chromosphere in millions of tiny spikes of hot gas called spicules.

19 Corona The corona is the final layer of the sun and extends several million miles outward from the photosphere. It can be seen best during a solar eclipse. The temperature of the corona averages 2 million degrees Kelvin.

20 Solar and Lunar Eclipses Solar and Lunar eclipses occur when the orbital motions of Earth and the Moon bring them into one line with the Sun. The lining up of Earth, Moon, and Sun only happens a handful of times per year.

21 Solar Eclipses Solar Eclipses occur when the Moon crosses the Sun as seen from Earth. An eclipse reveals one of the more astonishing coincidences in the natural world: seen from Earth, the Moon s disk almost perfectly matches the size of the Sun s disk. During a total solar eclipse, the Moon just blots out the sphere of the Sun, allowing us to view the Sun s corona.

22 Looking at this coincidence in detail The Sun is about 900,000 miles in diameter, and it lies, on average, about 93,000,000 miles away from Earth. The Moon is about 2,200 miles in diameter, and it lies on average, about 240,000 miles away from Earth. The ratio of the Sun s distance to its size is about 110 to 1 and so is the ratio of the Moon s distance to its size. Thus, the Sun and Moon happen to appear to be the same size in our sky.

23 Hundreds of millions of years ago, when the Moon was closer to Earth, it would have appeared larger than the Sun. In the future, when it is farther away, it will fail to blot out the whole disk of the Sun during eclipses. We just happen to be living at the right few-hundred million-year period to see this coincidence.

24 How big is the Sun? If the Sun was hollow, 1 million Earths would fit inside. Its mass is 1.99 x 10^30 kg (330,000 Earth masses)

25

26 Sunspots Dark, cool areas called sunspots appear on the photosphere. Sunspots always appear in pairs and are intense magnetic fields that break through the surface. Field lines leave through one sunspot and reenter through the other one. The magnetic field is caused by movements of gases in the sun s interior.

27 Sunspot activity occurs as part of an 11-year cycle called the solar cycle where there are periods of maximum and minimum activity. We are currently at the end of a minimum cycle.

28 Solar Prominences Occasionally, clouds of gases from the chromosphere will rise and orient themselves along the magnetic lines from sunspot pairs. These arches of gas are called prominences. They can last two to three months and can extend 30,000 miles or more above the sun s surface.

29 Solar Flares Sometimes in complex sunspot groups, abrupt, violent explosions from the sun occur. Solar flares are thought to be caused by sudden magnetic field changes in areas where the sun s magnetic field is concentrated.

30 Solar flares are accompanied by the release of gas, electrons, visible light, ultraviolet light and X-rays. When this radiation and particles reach the Earth s magnetic field, they interact with it at the poles to produce the auroras.

31 Solar flares can also disrupt communications, satellites, navigation systems and even power grids. A typical flare releases as much energy as a million hydrogen bombs.

32 The radiation and particles ionize the atmosphere and prevent the movement of radio waves between satellites and the ground.

33 Fate of the Sun The sun has been shining for about 4.5 billion years. It has enough hydrogen fuel to burn for about another 4-5 billion years. The size of the sun is a balance between the outward pressure made by the release of energy from nuclear fusion and the inward pull of gravity. When the core runs out of hydrogen fuel, it will contract under the weight of gravity. As the core contracts, it heats the upper layers causing them to expand.

34 As the outer layers expand, the radius of the sun will increase and it will become a red giant. The radius of the red giant sun will be just beyond the Earth s orbit, so the Earth will plunge into the core of the red giant sun and be vaporized.

35 At some point after this, the core will become hot enough to cause the helium to fuse into carbon. When the helium fuel has exhausted, the core will expand and cool. The upper layers will expand and eject material. Finally, the core will cool into a white dwarf. This entire process will take a few billion years.

36 As you can see, our sun is quite complex and interesting, and now you know more about how it produces the light and heat that all life on Earth depends on.